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Open AccessArticle

Nb and REE Distribution in the Monte Verde Carbonatite–Alkaline–Agpaitic Complex (Angola)

1
Departament de Mineralogia, Petrologia i Geologia Aplicada, Universitat de Barcelona, 08028 Barcelona, Spain
2
Geomar Enginyeria del Terreny SLP, 08015 Barcelona, Spain
3
Departamento de Geologia, Facultade de Ciências, Universidade Agostinho Neto, Luanda, Caixa Postal 815, Angola
4
Institut de Ciències de la Terra Jaume Almera, Consejo Superior de Investigaciones Científicas (CSIC), 08028 Barcelona, Spain
*
Author to whom correspondence should be addressed.
Minerals 2020, 10(1), 5; https://doi.org/10.3390/min10010005
Received: 31 July 2019 / Revised: 10 December 2019 / Accepted: 17 December 2019 / Published: 19 December 2019
(This article belongs to the Special Issue Mineral Deposits of Critical Elements)
The Angolan alkaline–carbonatite complex of Monte Verde has a semi-circular shape and is comprised of a central intrusion of foidolite rocks surrounded by concentrically arranged minor bodies of other alkaline rocks and carbonatite magmatic breccias. This rock association is hosted by fenitized Eburnean granites. Concentric swarms of alkaline dykes of late formation, mostly of nepheline trachyte composition, crosscut the previous units. Most high-field strength elements (HFSE) and rare earth elements (REE) are concentrated in pyrochlore crystals in the carbonatite and alkaline breccias. Magmatic fluornatropyrochlore is replaced and overgrown by five secondary generations of pyrochlore formed during subsolidus stages and have higher Th, REE, Si, U, Sr, Ba, Zr, and Ti contents. The second, third, and fourth pyrochlore generations are associated with late fluids also producing quartz and REE rich minerals; whereas fifth and sixth pyrochlore generations are linked to the fenitization process. On the other hand, minerals of the rinkite, rosenbuschite, wöhlerite, eudialyte groups, as well as loparite-(Ce), occur in accessory amounts in nepheline trachyte, recording low to moderate agpaicity. In addition, minor REE-bearing carbonates, silicates, and phosphates crystallize as late minor secondary minerals into carbonatite breccia and alkaline dykes. In conclusion, the scarcity of HFSE and REE minerals at the Monte Verde carbonatite-alkaline-agpaitic complex suggests low metallogenetic interest and economic potential for the outcrops analysed in this study. However, the potential for buried resources should not be neglected. View Full-Text
Keywords: Nb; pyrochlore; carbonatite; magmatic breccia; alkaline subsaturated rocks; agpaitic minerals; eudialyte; rinkite; loparite; Angola Nb; pyrochlore; carbonatite; magmatic breccia; alkaline subsaturated rocks; agpaitic minerals; eudialyte; rinkite; loparite; Angola
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Amores-Casals, S.; Gonçalves, A.O.; Melgarejo, J.-C.; Martí Molist, J. Nb and REE Distribution in the Monte Verde Carbonatite–Alkaline–Agpaitic Complex (Angola). Minerals 2020, 10, 5.

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